Devices for monitoring or analyzing gas (including moisture) have previously been proposed which use various measuring systems.
For example, the measuring systems employed in U.S. Pat. No. 4,724,700 to Jaasma and U.S. Pat. No. 4,507,875 to Hirsch et al. utilize a measured difference in gas flow rates before and after separation of a gaseous component, such as moisture. In Jaasma, the first flow rate measurement is made on partially dried gas; and in Hirsch et al., the first flow rate measurement is made on the entire starting gas.
In addition, U.S. Pat. No. 1,100,171 to Brown measures weight gain of a "moisture removing medium", Bergson (U.S. Pat. No. 3,051,643) utilizes an electrolysis cell and Roelse et al. (U.S. Pat. No. 4,102,647) uses an oleophilic substance which retains liquid hydrocarbon compounds. Moreover, infrared spectroscopy is being used in commercially available continuous moisture monitors to determine the moisture content of a sample.
Such prior art techniques and apparatus usually require trained personnel for operation, maintenance and repairs. Some of these systems are complex, and many are expensive to purchase, use and maintain, such as spectroscopic devices with their associated complex electrooptical assemblies. Others are not well-suited for continuous use or for use with automated and computerized controls, such as the systems which involve periodic measurement or monitoring, as described in the foregoing Brown and Roelse et al. patents.
A new and improved gas monitoring system is needed which uses simple, reliable mechanical hardware, requires little maintenance and repairs, and permits automated, computerized continuous operation. The present invention is directed to this need.